A U.S. Drug Enforcement Administration program to keep tabs on cars close to the U.S.-Mexican border has been gradually expanded nationwide and is regularly used by other law enforcement agencies in their hunt for suspects.

The extent of the system, which is said to contain hundreds of millions of records on motorists and their journeys, was disclosed in documents obtained by the American Civil Liberties Union as part of a Freedom of Information Act request. Much of the information disclosed to the ACLU was undated, making it difficult to understand the growth of the network, which is different from the cameras used to collect traffic tolls on expressways.

One of the undated documents said more than 100 cameras had been deployed in at least California, Arizona, New Mexico, Texas, Florida, Georgia, and New Jersey. The cameras snap each vehicle that passes, recording its license plate, the direction of travel and the time. Some cameras also snap a picture of the driver and passengers.

It was set up in 2008 and was opened to other law enforcement agencies in May 2009. Two years after it was launched, the system helped the DEA seize 98 kilograms of cocaine, 8,336 kilograms of marijuana and collect US$866,380. Its use was also expanded to the hunt for cars being driven by suspects in child abductions, rapes and other crimes.

Records on cars that don’t generate a “hit” in law enforcement investigations are said to be stored for six months—a period the ACLU said was “far too long.”

“The government should not collect or retain information revealing the movements of millions of people accused of no crime,” it said. “But even that long retention period is only meaningful if it comes with strict rules limiting data use, sharing, and access. Like its retention policy, the DEA should make these policies public.”